This invention relates to a tape drive for a magnetic tape machine with two tape reels which, depending on the transporting direction of the tape, act as take-up reel or as storage reel, the tape travelling from one to the other of these reels.
Such an arrangement is proposed in German Offenlegungsschrift (OS) 17 74 393. It is intended for use in a portable tape recorder and is to prevent the formation of loose tape loops during transportation of the switched-off instrument. A tension-sensitive locking device is provided for this purpose, which allows rotation of the storage-reel in the forward direction only when a predetermined tape tension exists. A unilaterally acting locking device is provided at the driving arrangement for the take-up reel, which permits a rotation of the take-up reel only in the forward direction.
The previously proposed mechanism retains the magnetic tape at a certain minimum tension when the machine is switched off, and also prevents the formation of tape-loops. However, it does not permit rewinding of completely or partially recorded tape, owing to the use of free-wheel clutches between the driving shaft of the take-up reel and the stationary components of the instrument; these clutches permit of only one direction of rotation for the drive shaft.
Rewinding is, however, required in portable magnetic tape recorders which are used for reporting purposes, and is necessary for the seamless joining of individual image scenes in the case of video tape. Moreover, the locking device in the previously proposed tape drive mechanism is complicated, both from the viewpoint of manufacturing costs and the susceptibility to trouble.